Electrolytic cell

ABSTRACT

Disclosed is an electrolytic cell for the continuous production of alkali metal chlorates from alkali metal chlorides having a cathode which includes a pervious plate with a surface that is sloped with respect to the vertical. Electrolysis takes place in the area between the anode end the pervious plate. Gaseous products produced adjacent the pervious plate are passed immediately through the openings in the pervious plate and out of the electrolizing area, thereby preventing gas blinding of the electrodes and producing circulation and back mixing of the solution within the cell.

United States Patent [72] Inventor Carl W. Raetuch Corpus Christi, Tex.

[21 Appl. No. 795,276

[22] Filed Jan. 30, 1969 [45] Patented Oct. 26, 1761 [7 3] Alsignee PPG Industries, Inc.

Pittsburgh, Pa.

[54] ELECTROLYTIC CELL 15 Clllms, 11 Dnwlng Fly.

[52] US. Cl 204/278, 204/2 70 [5|] lnLCI. 501k 1/00 [50] FleldolSeu-eh 204/95, 263, 266, 275, 278. 270

[56] lelerelces Cited UNITED STATES PATENTS 496,863 5/1893 Craney 204/266 1,302,824 5/1919 Marsh 204/266 1,471,641 10/1923 Adams 204/266 2,841,543 7/1958 Haller 204/278 X 3,344,053 9/1967 Neipert et al. 204/263 X 3,385,779 5/1968 Nishiba et a]. 204/95 X 3,5 l6,918 6/1970 Grother et al. 204/266 FOREIGN PATENTS 740.862 8/1966 Canada 204/253 Primary ExaminerF. C. Edmundson Attorney-Chisholm and Spencer ABSTRACT: Disclosed is an electrolytic cell for the continuous production of alkali metal chlorates from alkali metal chlorides having a cathode which includes a pervious plate with a surface that is sloped with respect to the vertical. Electrolysis takes place in the area between the anode end the pervious plate. Gaseous products produced ad jaccnt the pcrvious plate are passed immediately through the openings in the pervious plate and out of the electrolizing area, thereby preventing gas blinding of the electrodes and producing circulation and back mixing of the solution within the cell.

PATENTEDum 2 6 I911 SHEET 10F 4 INVENTOR CARL W. RAETZSCH ATTORNEYS no.2 Hm

PATENTEIJUET 26 Ian SHEET 3 BF 4 ATTORNEYS w m M CAFL W. RAETZ5CI/ m fi m,

PATENTEDUET 26 l9?| 3,515,4

' sum NF 4 CELL VOLTAGE VOLTS L llllllll 05101520253035 DEGREES FROM VERTICAL FIG. 1]

CELL VOLTAGE Vol-T5 w E" l l 4 a l l INVENTOR IO I5 20 25 30 DEGREES FROM VERT'CAL. CARL w. RAETZSLH BY M WLL ATTOR N 5Y5 ELECTROLYTIC CELL This invention relates to production of alkali metal chlorates from alkali metal chlorides and, in particular, to an electrolytic cell and to a method in which Iluid products are removed from the critical area between the electrodes and the solution is circulated within the cell.

Although the present invention is described in terms of its use in converting chlorides to chiorates, the invention is also applicable to use in the conversion of other halides to the corresponding halate and, in its broader aspects, to any similar electrolytic process in which it is desirable to remove buoyant fluid products from the interelectrode space. In the electrolysis of the alkali metal chlorides to form chlorates, hydroxyl ions are formed at the cathode and free chlorine is formed at the anode. A hypochlorite solution is formed upon intermixing of the hydroxyl ion and the free chlorine. The hypochlorite is subsequently oxidized to produce the alkali metal chlorate. The overall chemical reaction, for example, involving sodium chloride may be represented by the equation: SI-LO-NaCl N aCl0,+iI, T.

In the past, various provisions have been made for mixing and holding of the intermediate products during formation of the chlorate. One type of cell, disclosed in U.S. Pat. No. 3,350,286, for example, provides a pump that forces the solution between the electrodes and then into a tank where the solution is retained during the completion of the oxidation reaction. Another type of cell. disclosed in U.S. Pat. No. 3 ,38$,779, provides for circulation of the electrolyte between an electrolytic cell and an adjacent tank by the utilization of the product gases, principally hydrogen, which rise between the cathode and the anode. A further type of cell, shown in Canadian patent No. 740,862, has a plurality of tubular cathodes, each having a rod-shaped anode extending therethrough and spaced therefrom. The product gases cause the electrolyte to rise in said space between the anode and cathode as electrolysis takes place. Open tubes, called downcomer tubes, are located between adjacent cathodes whereby the electrolyte leaving the upper end of the electrodes is transported to the lower end of the electrodes so that it can pass once again therebetween.

One disadvantage is common to each of the abovedescribed cell structures; namely, that the product gases are permitted or required to pass upwardly between the cathode and anode. This produces what is typically termed "gas blinding. In other words, the accumulation of large amounts of gas bubbles and other cell products in the interelectrode space excludes the electrolyte from the interelectrode space which substantially increases the electrical resistance between the cathode and anode, thus increasing required voltage and decreasing cell power efficiency. The problem of gas blinding becomes substantially greater in cells operating at high temperatures and high-current density since the gas evolution is much more voluminous and rapid per unit of time. Such cells may, for example, contain sodium chlorate in a range of between 300 and 800 grams per liter, sodium chloride in the range of between 60 and 200 grams per liter, operate at a temperature of between 70 C. and I20 C. and at a current density of between about i and 4 amperes per square inch of cathode area. Gas produced adjacent the lower portions of the cathode rises in the interelectrode space-joining gas produced adjacent the upper portions of the cathode and, as would be expected, gas blinding is more noticeable as the upper ends of the electrodes are approached. Such gas blinding severely limits the height of the cell that can be economically used and increases the necessary spacing between the anode and cathode.

The present invention provides a new electrolytic cell structure for the production of chlorates in which the electrolytes may be circulated, mixed. and reacted entirely within the cell.

The circulation is produced by the rising gaseous products and yet the gaseous products are immediately removed from the critical space between the cathode and anode. The broader aspects. of the present invention apply to cells other than the chlorate cell. For example, the cell of the present invention may be employed in the electrolytic production oi lithium from a fused lithium salt. The present invention thus provides a more efficient cell, permits cells of greater height, and also permits closer spacing of the anode and cathode.

FIG. I is a perspective view of one embodiment of the present invention.

FIG. 2 is an exploded, perspective view of the embodiment shown in FIG. I.

FIG. 3 is a broken, vertical, cross-sectional view taken along the line Ill-III in FIG. I.

FIG. 4 is a cross-sectional view in FIG. 3.

FIG. 5 is an enlarged portion of FIG. 3.

FIG. 6 is another embodiment of the present invention.

FIG. 7 is an embodiment of the present invention in which the cell is substantially vertical.

FIG. 8 is an exploded view of a bipolar embodiment of the present invention.

FIG. 9 is an exploded view of a multielectrode, monopolar embodiment of the present invention.

FIG. 10 shows a line-graph oi cell voltage at various slopes.

FIG. I] shows a line-graph similar FIG. ill but at a different electrode spacing.

The present invention provides an electrolytic cell for the production of chlorates from chlorides. The cell has a substantially parallel cathode and anode. The cathode includes a backplate and a pervious plate which is spaced between the backplate and the anode. The pervious plate may be permeated by gaseous products and has a surface which is sloped with respect to the vertical so that the gaseous products liberated are immediately transported through the openings or channels in the pervious plate to a space provided between the backplate and the pervious plate and thus out of the critical area between the pervious plate and anode. The present invention may be provided in the form of a monopolar cell or a bipolar cell. Furthermore, the flow through the multielectrode embodiments may be either a series flow or a parallel ilow.

The chlorate cell 10 of the present invention, one embodiment of which is illustrated in FIGS. 1-5, may be supported by any suitable means; for example, as illustrated in FIG. I, the support means I5 includes a pair of spaced, horizontal base members II and I2 and a pair of upwardly extending side members I3 and Id. The cell 10 is positioned between the side members 13 and I4 and may be secured thereto by any conventional means; for example, by bolts (not shown).

The cell 10 (FIG. 2) is comprised of an anode l8 and a cathode assembly 19. The anode I! may be of any conventional structure and, preferably, includes a titanium base plate having an electrically conductive, anodically resistant coating. The coating may. for example, be comprised of one or a mixture of the platinum metals, such metals including ruthenium. rhodium, palladium, osmium, iridium, and platinum. The coating could, alternatively, be comprised of a platinum metal oxide, a mixture of platinum metal oxides, a mixture of a platinum metal and an oxide of an electrolytically film-forming metal such as titanium. or a mixture of a platinum metal oxide and another metallic oxide. For example, a mixture of ruthenium oxide and titanium oxide provides an excellent electrode coating. Any of various methods may be used for applying the coating to the titanium basepiate, typically precipitation of the metals or metallic oxides by chemical, thermal, or electrolytic methods. in certain cells the anode could be constructed of graphite, magnetite, or lead dioxide on a suitable substrate.

The cathode assembly l9 (FIGS. 2-5) is comprised of a bacltplate 22 and a pervious plate 23. The backplate 22 has a plurality of peripheral walls 24, 25, 26, and 27 which provide for spacing of the backplate 22 from the anode II and form a fluidtight enclosure. The pervious plate 23 may be comprised of any suitable material, such as iron, steel, or nickel, having the necessary electroconductive properties. The pervious plate 23 is of such a structure that iluids can readily pass therethrough. Typically. the pervious plate will be comprised taken along the line lV-IV of rod material, screen expanded metal mesh, perforated plate, or a louvered plate. The pervious plate 23 is spaced between the bacltplate 22 and the anode I8. If desired, the pervious plate 23 may be supported by the vertical peripheral walls 14 and 26 or, alternatively, may be secured to the bacltplate 22, as shown in FIG. 5, by the metal bars 28 and 29 which may be of steel. It may be desirable to terminate the pervious plate 23 at a point spaced downwardly from the upper peripheral wall 25 to facilitate better circulation of the solution within the cell.

Preferably, the pervious plate 23 is between 40 percent and 80 percent open and, more preferably, between 50 percent and 70 percent open. Operation within such preferred ranges provides increased power efficiency. The term "percent open" as used herein means the amount of open area as measured by the straight on shadow area method or, in other words, the amount of open area of the plate as compared to the total area of the plate expressed as a percentage. The "open area" of the plate is the portion of the plate through which the cell fluids can pass. The total area of the plate includes the open area plus the portion of the plate through which the fluids cannot pass. For example, a perforated plate having 5/32-inch holes on 7/32-inch centers provides a plate having 43 percent open area, as shown in table], and a pervious plate comprised of one-fourth-inch No. gauge expanded mesh provides 45 percent open area.

If the bacltplate 22 is spaced within a certain distance of the pervious plate, the backplate 22 can be made of a ferrous metal and will be cathodically protected by electrical energy that passes between the back plate and the anode, such energy passing through the open area of the pervious plate. The passing of electrical energy from the backplate through the open area of the previous plate to the anode will be hereinafter designated "electrical throw."

The spacing at which cathodic protection is present depends at least in part on the total electrical potential of the cell and on the percent of open area in the pervious plate. In order to provide the cathodic protection, the electrical potential between the bacltplate and the anode need not be great, providing the pervious plate is sufficiently open.

A voltage on the bacltplate of a chlorate cell as low as 0.3 volts may be sufficient to provide satisfactory protection. The maximum voltage on the bacltplate would be limited only to the maximum satisfactory voltage of the cell cathode which may be in the range of 1.5 to 3.0 volts. Thus the voltage on the bacltplate of a chlorate cell may, for example, be between 0.3 and 3.0 volts. The preferred voltage on the bacltplate has been found to be 0.9 volts.

Considerable latitude in the structure of the pervious plate, especially in the size of the openings, is permissible, consistent with certain underlying principles. The opening and the metal portions of the pervious plate must be small enough to provide even current distribution on the anode. On the other hand, the metal wires or web of the pervious plate 23 must be large enough to provide the necessary strength and rigidity. One perforate plate that was found to be highly satisfactory comprised a steel plate with l7/64-inch holes on SIIti-inch centers, thereby providing a plate having about 66 percent open area.

If desired, the bacltplate 22 could be coated with a chemically resistant costing, typically, plastic or rubber and. in such case, the spacing of the bacltplate 22 and pervious plate 23 could be made greater.

The anode could be provided with a pervious plate 23A similar to plate 23 as shown in FIG. 6. Such an anode 18A, however, would have to be coated with a suitable stable electrode material. notably a noble metal such as platinum. Pervious electrodes provide greater electrode surface per given external cell dimension than do electrodes of solid plate. Furthermore, they permit variation in the fluid volume of the cell, and they permit cells to be built of greater depth which is desirable from the standpoint of ease in connecting piping.

The anode l8 and the cathode I! serve in the present embodiment as the cell container. A separate cell container could be provided, however. The anode I8 and the cathode 19 are electrically insulated from each other by the insulating gasket 32 which may be of neoprene or tluoro carbon resin such as Teflon. The anode I8 and cathode [9 are secured together by any suitable means such as electrically insulated bolts 35 or clamps.

Electrical connections are provided on the anode l8 and the cathode I9 such as by conventional bus bars 37 and 38.

An interelectrode space 33 is provided between the anode 18 and the pervious plate 23 of cathode I9 in which electrolysis taltea place. The space 33 is preferably between 0. l and 0.5 inch in depth. Another space 34 is provided between the bacltplate 22 and the pervious plate 23 through which solution and gas may pass. The space 34 in the case of a high tempera ture chlorate cell is preferably between about 3 and 9 inches in depth.

The anode I8 and the cathode I9 are substantially parallel with one another and are supported in such a manner that they are sloped at an upwardly diverging angle with respect to the vertical. It has been found that the best results are obtained if the angle of slope is between 5' and 45, preferably between 10 and 25', although the benefits of the present invention can be obtained at greater or lesser angles. The cell could be positioned horizontally with the pervious plate 23 disposed above the anode.

A solution inlet line 39 is provided through which solution may be added to the cell 10, and a solution outlet or product pipe 40 is provided through which cell products such as hydrogen gas and solution containing sodium chlorate may be removed from the cell.

A solution containing sodium chloride may be added to the cell I0 through inlet line 39 until the cell is substantially filled. The solution may be the mother liquor from an external product crystallizer in which case the solution, in addition to sodium chloride, would contain other materials, such as sodium chlorate. Also, the solution could be passed through an external circuit for temperature and pi! control. The cell l0 may be operated, typically, under the following cell conditions:

Concentration of cell solution Sodium chlorate 300-800 grams/liter Sodium chloride 60-200 grams/liter Temperature 70'-l 20 C.

Current density loll-600 amp/ft.

The anode l8 and the cathode I9 are connected to an electrical source (not shown). An electrical potential is set up principally between the anode II and the pervious plate 23 of cathode 19. As water and sodium chloride pass between the anode ll and the pervious plate 23, electrolysis takes place and hydrogen gas and sodium chlorate are produced.

Hydrogen and water vapor gases and some oxygen and chlorine rise in the cell as is shown by the small bubbles 4] in FIG. 5. passing through the pervious plate 23 and upwards in the space or passage 34 to the top of the cell. By so doing, the gnes are immediately removed from the critical space 33 where electrolysis takes place, and thereby gas blinding is prevented or substantially reduced. Moreover. as the gases rise, circulation of the solution in the cell is produced, as illustrated by the arrows in FIG. 5. thereby preventing depletion of chloride ions in the critical electrolyzing space 33 and further preventing an excessive accumulation of hypochlorite and chlorate ions adjacent the anode.

The product stream from the cell may be passed through an external product crystallizer where a portion of the sodium chlorate is removed. The mother liquor from the external product crystallizer may be fortified with sodium chloride, reheated, and returned to the cell for further electrolysis.

The cell 50, illustrated in FIG. 7, is another embodiment of the present invention. The cell 50, however, is disposed in a substantially vertical position. The cell 50 is comprised of an anode 5i and a cathode 52. The anode SI may be identical to the above-described anode ID. The cathode 52 is comprised of a bacltplate 53 and a pervious plate The bacltplate 53 may be very similar to backplate 12. The pervious plate 54. however, is of a louvered construction, having portions of its surface sloped with respect to the vertical. The cell 50 may be connected to feed and product lines and an electrical source in a manner similar to cell 10.

The operation of the cell 50 is substantially identical to the cell i0 except that the gas formed at the cathode is removed from the space between the cathode and anode by the sloped louvers. The hydrogen gas which comprises approximately 95 percent of the gas electrochemically produced and approximately 25 to 35 percent of the total gas produced in the cell is formed adjacent the surface of the louvers, such as 57 and 58. The gas rises until it strikes the lower surface of a louver and then moves along the lower surface until it reaches the back space 59. The movement of the hydrogen gas and the solution is otherwise the same as above described with respect to the cell I0.

The principal of cell 50 is also well suited for the electrolytic production of lithium metal from a fused lithium salt. Since the fluid lithium metal is less dense than the fluid lithium salt, it would rise in a conventional cell in a manner similar to that of hydrogen gas in the chlorate cell. The presence of substantial amounts of lithium and chlorine in the interelectrode space tends to reduce the current efficiency due to reaction between the lithium and chlorine. In cell 50 the fluid lithium metal is formed at the surface of louvers 57 and 58 and is removed from the critical space between the anode and the pervious plate in the same manner as hydrogen is removed in the chlorate cell.

The above-described cells I0 and 50 can be provided in the form of multiple electrode cells, such as shown in FIGS. 8 and 9. The cell I10 (FIG. 8) is a bipolar cell and has a plurality of electrodes 1 II, I "A, l I I8, and I I IC. The electrode 111 serves as a cathode half cell and electrode IIlC serves as an anode half cell. The intennediate electrodes, II IA and U15, each has a first side III which serves as an anode and a second side I13 which serves as a cathode. Each of the electrodes which provide a cathode includes a pervious plate 114 which may be identical to either one of the above-described pervious plates 23 or 54. Those portions of the electrodes 111A, 1118, and 111C which serve as anodes may be made of titanium or other material suitable for anodic conditions and coated with a suitable electrode material, such as a platinum coating. A convenient method of constructing the electrodes III-IIIC is to employ a titanium metal clad steel plate, the titanium metal being platinized and serving as the anode, titanium metal in this case meaning any of the anodic self-protective metals including tantalum, niobium. and titanium.

As shown in FIG. 8, the cell Ill) may be provided with a parallel flow of solution between the various electrodes. However, if desired, the flow of solution through the multielectrode cell could be provided in series merely by moving outlet lines such that they extend between cell compartments, thereby requiring the solution to pass sequentially through each of the cell compartments.

A multielectrode cell 210 may be provided of a monopolar type, as shown in FIG. 9. The cell 210 includes a plurality of anodes ZII, 211A, ZIIB. and a plurality of cathodes 212, 212A, 2128. In this case, a pair of insulating gaskets are provided, one on either side of the electrodes, insulating the same from the adjacent electrodes. For example. anode ZII is insulated from cathode 212 by insulating gasket 214 and from the cathode 212A by insulating gasket 215. As shown in FIG. 9, anodes ZII, ZIIA, and ZIIB are connected to an electrical source of negative electrical potential, and the cathodes 212, 212A, and 2128 are connected to an electrical source of positive potential. The cell 210 may be provided with either a parallel flow or a series flow of solution.

EXAMPLE 1 FIGS. 10 and II illustrate the effect that sloping the cell has on the voltage of the cell (i.e., the difl'erence in potential between the anode and the pervious plate). The results shown in FIG. I0 were obtained a cell substantially like the one shown in FIGS. 1-5. The internal dimensions were i foot in width, 1% inches in depth, and 4 feet in height. The cell had an active anode area of 4 by 30 inches or 120 square inches. The cathode has a mesh of 37 percent area and the anode was a platinized titanium electrode. The interelectrode space was one-eighth inch in depth and the current density was 500 amps per square foot. The cell was set up in such a manner that a feed stream could be continuously fed into the cell and a product stream could be continuously removed from the cell. The concentration of the feed stream was: sodium chlorate, 502 grams per liter; and sodium chloride, l 19 grams per liter. The concentration of the solution within the cell was maintained within the range: sodium chlorate, from 600 to 800 grams per liter; and sodium chloride, from to 100 grams per liter. The pH of the feed stream was maintained between 6.1 and 6.3. The feed solution was heated to about C. so that the temperature within the cell, as measured at a point 4 inches below the top of the cell, remained between I00 and 105 C. In this example, the best voltages were obtained at an angle of about 2$to 30 from the vertical, although a material elfect is noted even at an angle of 5 from the vertical.

EXAMPLE II The results shown in FIG. 11 were obtained in the cell used in example 1 and under similar cell conditions except that the interelectrode spacing was changed to one-fourth inch. The concentration of the feed stream was: sodium chlorate, $8l grams per liter; and sodium chloride, I08 grams per liter. The pH of the feed stream was between 6.I and 6.3. The concentration of the sodium chlorate within the cell was maintained within the range of 600 to 800 grams per liter and sodium chloride between 90 and grams per liter. The temperature within the cell was maintained between 100 and C. In this example, the effect of sloping the cell is particularly noticeable at angles of between about l0 and about 25 The best results obtained here were at angles of about 15' to 20' from the vertical where a voltage advantage of approximately 0.15 was obtained.

EXAMPLE III The following example illustrates the effect various degrees of open area of the pervious plate has on the pervious plate potential and on backplate potential. This example also shows the effect of various spacings between the pervious plate and the backplate A small laboratory cell was operated with the cathode at a slope of 23 from the vertical. The test electrodes were circular, having a l l3/l 6-inch diameter. The anode-topervious plate spacing was one-eighth inch, and the pervious plate-to-backplate spacing was 6 inches. The anode current density was 500 amperes per square foot of pervious plate. The cell temperature was I05 C. The solution used contained 46.5 percent sodium chlorate and 6.l percent sodium chloride.

The results obtained in the cell using pervious plates of various degrees of open area are shown in the following table. In this instance, the best results were obtained at 66 percent open area with a perforated plate.

'IABLE 1 0 PBI'VIIOItIS Bfatik ae pae a e: pomitlal, potential, Type of periorated plate 1 percent volts 1 volts 1 dash holes a tat-inch centers x anti-inch thickness 1. 01 (L 64 winch holes 1 i ls-inch centers s (HIM-inch thlckmss 46 1. ill 0. 90 1c4nch holes x 96-inch centers s ILWZO-Inch mm 01 1. 67 0. ill ids-inch holes x Hs-lnch centers 1 (MIMI-inch thickness es 1. 54 0. 99

l Electrode potential measurements were made conventionally using a Ag/AgCl reierenee electrode connected to a lugglnfirobo by means 0 a "salt bridge" containing 18 percent NaClm, an 6 percent NsCl. nitsge measuremmts were made with a high impedance digital volt meter which read directly to i mlllivolt.

The above-described cell, using a pervious plate of the perforated type having 66-percent open area, was operated with the backplate spaced at various distances from the pervious plate. All other cell conditions remained the same. At inches the backplate potential was 101 volts, at 6 inches the potential was 0.99, and at 8 inches the potential was 0.88. in each instance the backplate received sufficient cathodic protection to prevent corrosion of the ferrous metal.

Although the present invention has been described with reference to the specific details of particular embodiments thereof, it is not intended thereby to limit the scope of the invention except insofar as the specific details are recited in the appended claims.

What is claimed is:

1. An electrolytic cell comprising fluid-containing means including fluid inlet and outlet means, an anode and cathode disposed in said fluid-containing means, said anode comprising an impervious plate, said cathode being spaced from said anode and comprising a pervious plate, said pervious plate having at least portions thereof which are disposed at an upwardly diverging angle with respect to the vertical, the openings in said pervious metal plate providing channels which lead upwardly and away from said anode, whereby buoyant products formed between said pervious plate and said anode are caused to pass through said channels and away from the space between said pervious plate and said anode.

2. An electrolytic cell as defined in claim 1 wherein said buoyant products are gaseous products and wherein said cathode includes an impervious backplate and wherein the pervious plate is supported by said backplate plate, said pervious plate and said backplate defining therebetween a space through which said gaseous products may rise and through which cell fluids may pass thereby promoting circulation.

3. An electrolytic cell as defined in claim 2 wherein said anode and said cathode are disposed at an upwardly diverging angle with respect to the vertical.

4. An electrolytic cell as defined in claim 3 wherein the space between said pervious plate and said anode is between 01 and 0.5 inch and wherein said upwardly diverging angle is in the range of IO to 25.

5. An electrolytic cell as defined in claim 3 wherein the space between said pervious plate and said anode is about one-fourth inch and wherein said upwardly diverging angle is in the range of l5 to 6. An electrolytic cell as defined in claim I wherein said anode is vertically disposed and said cathode has surface portions comprising louvers which are sloped with respect to the vertical.

7. An electrolytic cell as defined in claim 1 wherein said anode and cathode each comprises a pervious plate and an impervious plate, said plates being substantially parallel and said anode and cathode being substantially parallel.

I. An electrolytic cell as defined in claim 3 wherein the space between said pervious metal plate and said anode is between 0.1 and 0.5 inch and wherein the open area of said pervious metal plate comprises in the range of between 40 and 80 percent of said plate.

9. An electrolytic cell as defined in claim 9 wherein the open area of said pervious metal plate is in the range of between 50 and 70 percent.

10. An electrolytic cell as defined in claim 8 wherein said cell is for the production of alkali metal chlorates from alkali metal chlorides and wherein the backplate is of ferrous metal and is spaced sufficiently near the pervious plate and said anode to provide a potential on said backplate of at least 0.9 volts.

11. An electrolytic cell for production of alkali metal chlorates from alkali metal chlorides, said cell comprising:

an anode comprising an impervious titanium rneta'l plate having an electrically conductive, anodically resistant coating,

a cathode comprising a ferrous metal backplate and a pervious metal plate, said pervious metal plate comprising a perforated metal plate which is supported by and electrically interconnected to said backplate said pervious metal plate being spaced between said bacltplate and said anode;

said anode, cathode backplate and cathode pervious plate being substantially parallel with one another and being disposed at an angle of between I0 and 25 with respect to the vertical, said cathode being an erior to said anode; Insulating and sealing means dispose between said anode and said cathode back plate, around the periphery thereof, thereby defining a fluid-containing chamber;

inlet and outlet means for passage of fluid into and out of said chamber;

means for applying an electrical potential to said anode and cathode;

wherein electrolysis takes place in the space between said pervious metal plate and said anode and wherein gaseous products produced during electrolysis pass upwardly through said pervious plate out of said electrolyzing space and then upwardly in said space between the pervious plate and the backplate thereby producing cell circulation and preventing said gas from blinding the anode and cathode.

l2. An electrolytic cell comprising fluid-containing means including fluid inlet and outlet means, an anode and cathode electrode pair disposed in said fluid-containing means, said cathode being spaced from said anode. providing therebetween an interelectrode space for electrolysis to take place in, at least one electrode of said pair comprising a pervious metallic plate, said pervious plate electrode being sloped in the cell at an upwardly diverging angle with respect to the vertical, the openings in said pervious metal plate electrode providing channels which lead upwardly and away from said other electrode of the pair whereby buoyant products formed between said pervious plate and said other electrode pass through said channels and away from the space between said pervious plate and said other electrode.

13. An electrolytic cell as defined in claim [2 wherein said pervious metal plate electrode is comprised of a material selected from the group consisting of screen, expanded metal mesh and perforated metal plate.

14. An electrolytic cell as defined in claim 12 wherein said upwardly diverging angle is in the range of 10' to 25'.

15.,An electrolytic cell as defined in claim 12 wherein the cell comprises a' plurality of unit cells in series, at least two adjacent of said units having an electrode and cathode pair one of which is a pervious electrode sloped at an upwardly diverging angle with respect to the vertical and providing the said channels as specified in claim l2, s backplate spaced from and providing a fluid tight enclosure on the side of the pervious electrode remote from the opposed electrode of the pair of said unit, said backplate being in electrical contact with an electroconductive surface opposed to the pervious electrode of said adjacent unit.

. I i i i mg UNITED "STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 616,444 Dated October 26, 1971 Inv nt flp) jarl W. Raetzsch It; is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On Title Page, column 11 "Patented Oct. 26, 1761",

should read --Patented Oct. 26, l97l- In Claim 2, column 7, line 30, after "backplate",

delete the word 'plat e" which is repeated.

In Claim 4, column 7', line 39, 901" should read In Claim 9, column 7, line 58, after "defined in",

"Claim 9" should read "claim 8--.

Signed and sealed this 6th day of June 1972.

(SEAL) I Attest:

EDWARD M. FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

2. An electrolytic cell as defined in claim 1 wherein said buoyant products are gaseous products and wherein said cathode includes an impervious backplate and wherein the pervious plate is supported by said backplate plate, said pervious plate and said backplate defining theRebetween a space through which said gaseous products may rise and through which cell fluids may pass thereby promoting circulation.
 3. An electrolytic cell as defined in claim 2 wherein said anode and said cathode are disposed at an upwardly diverging angle with respect to the vertical.
 4. An electrolytic cell as defined in claim 3 wherein the space between said pervious plate and said anode is between 01 and 0.5 inch and wherein said upwardly diverging angle is in the range of 10* to 25*.
 5. An electrolytic cell as defined in claim 3 wherein the space between said pervious plate and said anode is about one-fourth inch and wherein said upwardly diverging angle is in the range of 15* to 20*.
 6. An electrolytic cell as defined in claim 1 wherein said anode is vertically disposed and said cathode has surface portions comprising louvers which are sloped with respect to the vertical.
 7. An electrolytic cell as defined in claim 1 wherein said anode and cathode each comprises a pervious plate and an impervious plate, said plates being substantially parallel and said anode and cathode being substantially parallel.
 8. An electrolytic cell as defined in claim 3 wherein the space between said pervious metal plate and said anode is between 0.1 and 0.5 inch and wherein the open area of said pervious metal plate comprises in the range of between 40 and 80 percent of said plate.
 9. An electrolytic cell as defined in claim 8 wherein the open area of said pervious metal plate is in the range of between 50 and 70 percent.
 10. An electrolytic cell as defined in claim 8 wherein said cell is for the production of alkali metal chlorates from alkali metal chlorides and wherein the backplate is of ferrous metal and is spaced sufficiently near the pervious plate and said anode to provide a potential on said backplate of at least 0.9 volts.
 11. An electrolytic cell for production of alkali metal chlorates from alkali metal chlorides, said cell comprising: an anode comprising an impervious titanium metal plate having an electrically conductive, anodically resistant coating, a cathode comprising a ferrous metal backplate and a pervious metal plate, said pervious metal plate comprising a perforated metal plate which is supported by and electrically interconnected to said backplate, said pervious metal plate being spaced between said backplate and said anode; said anode, cathode backplate, and cathode pervious plate being substantially parallel with one another and being disposed at an angle of between 10* and 25* with respect to the vertical, said cathode being superior to said anode; insulating and sealing means disposed between said anode and said cathode back plate, around the periphery thereof, thereby defining a fluid-containing chamber; inlet and outlet means for passage of fluid into and out of said chamber; means for applying an electrical potential to said anode and cathode; wherein electrolysis takes place in the space between said pervious metal plate and said anode and wherein gaseous products produced during electrolysis pass upwardly through said pervious plate out of said electrolyzing space and then upwardly in said space between the pervious plate and the backplate thereby producing cell circulation and preventing said gas from blinding the anode and cathode.
 12. An electrolytic cell comprising fluid-containing means including fluid inlet and outlet means, an anode and cathode electrode pair disposed in said fluid-containing means, said cathode being spaced from said anode, providing therebetween an interelectrode space for electrolysis to take place in, at least one electrode of said pair comprising a pervious metallic plate, said pervious plate electrode being sloped in the cell at an upwardly diverging angle with respect to the vertical, the openings in said pervious metal plate electrode providing channeLs which lead upwardly and away from said other electrode of the pair whereby buoyant products formed between said pervious plate and said other electrode pass through said channels and away from the space between said pervious plate and said other electrode.
 13. An electrolytic cell as defined in claim 12 wherein said pervious metal plate electrode is comprised of a material selected from the group consisting of screen, expanded metal mesh and perforated metal plate.
 14. An electrolytic cell as defined in claim 12 wherein said upwardly diverging angle is in the range of 10* to 25*.
 15. An electrolytic cell as defined in claim 12 wherein the cell comprises a plurality of unit cells in series, at least two adjacent of said units having an electrode and cathode pair one of which is a pervious electrode sloped at an upwardly diverging angle with respect to the vertical and providing the said channels as specified in claim 12, a backplate spaced from and providing a fluid tight enclosure on the side of the pervious electrode remote from the opposed electrode of the pair of said unit, said backplate being in electrical contact with an electroconductive surface opposed to the pervious electrode of said adjacent unit. 